Good day, girls The baby often has a rash on his face, like eczema. I …

Good day, girls The baby often has a rash on his face, like eczema. I wanted to know how the blood test procedure works to check for what exactly the child's allergy is? I just excluded sweets from the diet and removed eggs and other things. I can't figure out what it is? I moisturize with Aqualan cream and it passes. After some time, he starts to break out again I don't even know what to do anymore ?.